Gas analysis is used to determine its qualitative and quantitative composition. This includes the constituents or properties of a gas (either pure or mixed). Composition can be measured by chemical adsorption, combustion, electrochemical cells, indicator papers, chromatography, mass spectroscopy, etc. Chemical gas analysis Properties analysed include heating value, molecular weight, density, and viscosity. There are chemical, physicochemical, and physical methods of gas measurement / analysis. The chemical methods are based on the principle of the absorption of components of a gas mixture by various reagents. A benefit of chemical methods is the relative simplicity of the gas analyser itself. In physicochemical methods of gas analysis, the components of a gas mixture are absorbed by a solution of a suitable reagent. The electrical conductivity, optical density, or other physicochemical properties of the solution are then measured. Physical gas analysis Physical methods of analysis are based on the changes in the physical properties of a gas mixture that vary with its composition: density, viscosity, boiling point, thermoconductivity, the emission or absorption of light (spectral analysis), and mass spectra (mass spectroscopy).